A 20 oz denim is not going to bend and move for most garment uses. A 5 oz denim is not going to provide heavy denim jeans or jackets, however it will make wonderful shirts, skirts and dresses that will drape well. Knowing that denim runs from 5 to 20 oz and that the less the weight, the lighter, softer, loft the denim will have, you can purchase or request samples of the weights you believe are in the scope you are looking for.
Looking at the samples in the photo, an 8oz denim is just a tad more pliable and soft than the 9 oz. The 9 oz sample is just a tad more pliable and soft than the 10 oz sample. Durability wise they are pretty much identical. The real difference comes in at the drape and flexibility.
Traditionally, 12 to 14 oz is used for denim jeans. It will not ruffle or drape if you were making a full skirt say for square dancing.